Got a few servo wires, as well as the 'servo' wire for my ESC that I wana shorten, just looking for the best way to do it...

Firstly, its OK to shorten these wires isnt it? Brushed and BL ESC...

Now, Im thinking, just cut a piece out of the middle area of the wire, to shorten it. Then just solder the 3 wires together, idividually heatshrink them, then put a piece of larger heatskrink round the 3 wires to keep them together.
Does that sound like a good plan, or are there any other better ways?

If you are doing this to save weight, don't, you won't unless you remove a lot of wire.
I would do as you mentioned until the three wires are soldered/shrunk. Then add some hot glue over the area on both sides keeping it thin. It won't take much heat glue to satisfy your eyes.